U.S. Pat. No. 4,540,236 discloses an automatic locking device for a plug of a coaxial electrode line which is to be connected to a cardiac pacemaker. The device has hooked holding claws which engage into an annular groove at the tip of the plug and thereby provide that the plug connection is safeguarded in relation to axial tensile loadings. In order to be able to remove the plug from the connecting arrangement, pressure has to be applied manually from the end of the header in order to cause the holding claws to spread apart, by way of a linkage.
In addition, U.S. Pat. No. 5,252,090 discloses a self-locking plug connection for the plug of an implantable coaxial electrode line which has a connecting arrangement with an electrical contact element that has a plurality of resilient, substantially radially inwardly facing tongues which are urged radially outwardly by the tip of the plug against the spring force and produce a clamping force when the plug is pushed into the connecting arrangement. The electrical contact element has additional, inclinedly outwardly directed spring arms by which the clamping contact of the inwardly facing tongues at the tip of the plug can be disengaged when those spring arms are loaded from the exterior by a pressure force.
Furthermore, U.S. Pat. No. 5,697,804 discloses a cardiac pacemaker having a locking device in which the electrical contact element is in the form of a coil spring. By virtue of a rotary movement of the plug of the electrode line which is to be connected to the cardiac pacemaker, within the connecting arrangement, the diameter of the coil spring can be reduced to such an extent that a clamping action is produced between the individual turns of the coil spring and the peripheral surface of the deferent pole of the plug.
The known locking devices which are of a relatively complicated structure suffer from the disadvantage that they are very difficult to handle in service thereof, in particular when releasing the locking action, as the locking devices can only be released by a pressure force which is to be applied manually frontally or laterally from the header wall. In addition there is the disadvantage that it is not possible to see whether the plug disposed in the connecting arrangement has also actually been locked.
Finally, international patent application WO 98/57702 discloses a screw-free connecting system for connecting at least one electrode line to a cardiac pacemaker. The header of the cardiac pacemaker has a locking device with a hand lever connected to a stepped shaft, for locking a connected electrode line. The shaft which is rotatable by the hand lever extends transversely with respect to the axis of the bore or bores provided for insertion of the electrode line, and has, distributed at its periphery, saddle-shaped recesses of different depths which are disposed in pairs in mutually orthogonally opposite relationship. In the open position of the locking device the large recesses in the rotatable shaft form a part of the bore wall and bear against the sheathing of the electrode line or lines. By virtue of pivotal movement of the hand lever the smaller recesses in the shaft come into operative contact with the sheathing of the electrode line or lines, with a reduction in the free cross-section of the bore, and block the electrode line or lines to prevent axial movement, by virtue of a clamping action.
That locking device is in the form of a complicated shaped component and suffers from the further disadvantage that the clamping action of the shaft for holding the plug or plugs is limited to the region of the insulation of the electrode line. As a result, the arrangement essentially only affords a mechanical safeguard in relation to tensile forces acting on the electrode line, without the actual contact locations having to be inevitably secured. It is therefore not possible to have any information about the quality of the contacting action if the plug of the electrode line for example does not reach or only partially reaches the contact region which is provided for same, after insertion of the line. In addition, there is the disadvantage that damage to the wire strands in the line or a short-circuit between individual strands cannot be reliably excluded.